In one known leading/trailing edge drive system a torque limiting device is used to protect an actuator and associated structure from a full stall/dynamic torque applied by power drive source. Other known systems also include torque limiting devices. There exist several types of such known torque limiting devices. Examples of such types of known systems include spring-wrap brakes, multi-disk brakes, and shear-outs. Also, a known leading/trailing edge drive system includes an antiback-up device, often referred to as a no-back, which prevents reverse motion in the event of a shaft failure.
Turning to some specifics of the known devices, the spring-wrap brake device relies on a spring expanding into a housing to absorb the torque. Viscous drag is very high in the spring-wrap brake device. Within the multi-disk brake torque limiting device, several disks are pressed against each other via the use of a ball and ramp configuration or the like. In order to avoid issues concerning freeze-up, lubrication is provided to the disk brake pack. However, such lubrication may cause considerable viscous drag. Such viscous drag is not problematic so as long as the drag is accurately predicted and accounted within a torque brake setting, etc. However, the drag causes inefficiency in the system and higher limit loads on components downstream of the torque brake. With regard to shear-outs, replacement is needed subsequent to the shearing. All of the known devices are actuated via mechanical arrangement or connection. Also, most of the known mechanical systems include the use of an associated antiback-up (i.e., no-back) device.
In general, torque limiting devices must operate in severe environments including wide extremes of temperature, altitude, and weather. In addition, torque limiting devices are often used on high performance aircraft where severe vibration also occurs. Aircraft operating in such conditions put high demand loads on the control surfaces and subsequently, the associated actuation system. Accordingly, the need for torque limiting devices is readily apparent.
It is desirable to have a torque limiting device that operates reliably and swiftly. It is desirable to have a torque limiting device that eliminates the need for a no-back device. Also, it is desirable to prevent inadvertent lock-outs due to inertia or load spikes. In addition, it is desirable to have a torque limiting device that includes a reduced sensitivity range and reduces the occurrence of low temperature breakout torque penalties. It is also desirable that the size of the actuators used be reduced.